(a) Field of the Invention
The present invention relates to a pump device, for example, used in a power steering apparatus which provides a steering force or a steering assistance force for a steering mechanism of an automotive vehicle by an operation of a hydraulic (or hydraulic pressure) power cylinder in accordance with a steering torque outputted from the steering mechanism of the automotive vehicle.
(b) Description of the Related Art
A previously proposed pump device is exemplified by a Japanese Patent Application First Publication (tokkai) No. 2004-276664 published on Oct. 7, 2004 in which the previously proposed pump device is applied to a power steering apparatus. The disclosed power steering apparatus includes: a steering shaft attached onto a steering wheel; an output shaft connected with a lower end of the steering shaft; a rack-and-pinion mechanism installed on a lower end of the output shaft; a hydraulic (pressure) power cylinder interlinked with a rack of the rack-and-pinion mechanism; a reversible pump which relatively supplies a working oil to first and second hydraulic pressure chambers located at left and right sides of the hydraulic pressure power cylinder via first and second passages; and a control valve which is a return check valve installed in a bypass passage connected between the first and second passages.
This control valve is configured to have a working oil which is drained from a reversible pump supplied to the hydraulic pressure power cylinder in response to a closure of a pressure application side (or pressurization side) valve and, while, have the working oil within the hydraulic power cylinder exhausted to a reservoir tank in response to an open of a non-pressure application side (non-pressurization side) valve. This exhaust action causes an efficient reduction in the hydraulic pressure at the non-pressure application side (non-pressurization side) and causes such contaminations and air as metallic powders present in piping to be exhausted within the reservoir tank.
Then, if, during a vehicular run, an ordinary leftward (counterclockwise) or rightward (clockwise steering through the steering wheel is carried out, a detection mechanism detecting this steering torque according to the steering operation causes the reversible pump to normally or reversely revolve via an electronic controller so that the working oil in either one of the first and second hydraulic pressure chambers and within either one of the first and second communication passages is selectively supplied to the other of the first and second hydraulic pressure chambers and within the other of the first and second communication passages.